Most fire departments respond within the first 5 min of notification of a fire. If fire victims are found at that stage by the firefighters, then incapacitation or death has occurred during the initial low-energy phase where smoke is being produced. Studies have shown that during this initial low-energy phase of the fire, gases commonly thought responsible for incapacitation or death are frequently not present in concentrations adequate to cause this result. In the current study free radicals, measured by electron spin resonance spectroscopy, were trapped in concentrations that we consider incapacitating, thus providing an explanation for “incapacitation without cause.” This finding points the way to the design of more efficient temporary protective equipment for those who are in a high fire hazard environment, such as airline passengers, and suggests the idea of establishing a thermodynamic marker for the relative toxicity of building materials.